000
FXUS66 KSEW 271059
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PST FRI FEB 27 2015
.SYNOPSIS...A WEAK WEATHER SYSTEM WILL PRODUCE WIDESPREAD SHOWERS
ACROSS WESTERN WASHINGTON TODAY AS IT MOVES SOUTHEAST FROM THE COAST
TOWARD OREGON. A FEW INCHES OF SNOW WILL FALL IN THE MOUNTAINS. AN
UPPER RIDGE AND OFFSHORE FLOW WILL BRING SUNNY DAYS AND COOL NIGHTS
THIS WEEKEND. A WEAK SYSTEM WILL MOVE THROUGH SUNDAY NIGHT AND
MONDAY...WITH DRY WEATHER AGAIN TUESDAY AND WEDNESDAY.
&&
.SHORT TERM...A SMALL UPPER LOW THAT WAS NEAR THE NORTH TIP OF
VANCOUVER ISLAND MOVED SOUTHEAST INTO THE WASHINGTON COASTAL WATERS
OVERNIGHT. THIS FEATURE PRODUCED WIDESPREAD LIGHT TO MODERATE
SHOWERS ACROSS WESTERN WASHINGTON OVERNIGHT...WITH MORE THAN 0.25
INCH OF PRECIPITATION IN MANY PLACES. AT 2 AM THE SHOWERS WERE
MAINLY IN A BAND OVER THE INTERIOR LOWLANDS WITH TEMPERATURES IN THE
MID 40S TO LOWER 50S.
THE UPPER LOW WILL CONTINUE ITS SOUTHEAST TRACK...MOVING INTO
NORTHWEST OREGON TODAY AND SOUTHEAST OREGON OR NORTHWEST NEVADA
TONIGHT. THE UPPER FLOW OVER WESTERN WASHINGTON WILL VEER TO NORTH
AND THEN NORTHEAST...AND NORTHERLY OFFSHORE LOW LEVEL FLOW WILL
DEVELOP TOO AS SURFACE HIGH PRESSURE MOVES SOUTH ACROSS BRITISH
COLUMBIA.
SHOWERS SHOULD REMAIN FAIRLY WIDESPREAD TODAY...ESPECIALLY THIS
MORNING...BUT THEY WILL DECREASE FROM NORTH TO SOUTH LATE TODAY AND
TONIGHT AS THE DRY AND COOLER NORTHERLY FLOW TAKES OVER. BY LATE
TONIGHT SKIES WILL BE CLEARING...WITH LIGHT SPOTTY SHOWERS LIMITED
TO THE SOUTH PART OF THE FORECAST AREA AND PERHAPS A WEAK
CONVERGENCE ZONE. BREEZY NORTH OR NORTHEAST WINDS WILL DEVELOP
TONIGHT...WITH THE STRONGEST WINDS IN THE NORTH INTERIOR NEAR THE
FRASER RIVER OUTFLOW SOURCE.
THE SNOW LEVEL WILL BE 3000 TO 3500 FT TODAY...THEN FALL SLIGHTLY
TONIGHT AS PRECIPITATION DECREASES. ANOTHER 2 TO 5 INCHES OF SNOW IS
LIKELY IN THE MOUNTAINS WITH THIS SYSTEM...WITH THE HEAVIEST AMOUNTS
IN THE OLYMPICS AND THE CASCADES SOUTH OF SNOQUALMIE PASS.
DRY NORTHERLY FLOW ALOFT WILL PREVAIL SATURDAY FOR A SUNNY DAY.
TEMPERATURES SHOULD CLIMB INTO THE LOWER 50S IN THE LOWLANDS...BUT
NORTHERLY OFFSHORE SURFACE FLOW WILL MAKE FOR BREEZY CONDITIONS
ACROSS MUCH OF THE FORECAST AREA. WINDS SHOULD EASE SATURDAY
NIGHT...WITH OVERNIGHT LOWS IN THE 30S AND LOCALLY BELOW FREEZING
UNDER MOSTLY CLEAR SKIES.
SUNDAY WILL BE ANOTHER DRY AND MOSTLY SUNNY DAY...BUT THE UPPER FLOW
WILL BACK TO NORTHWEST AS A WEAK UPPER SHORTWAVE STARTS APPROACHING
ALONG THE COAST OF BRITISH COLUMBIA. THE SHORTWAVE WILL MOVE ACROSS
WESTERN WASHINGTON SUNDAY NIGHT. IT WILL BRING A CHANCE OF
PRECIPITATION...BUT THE LATEST MODEL RUNS SUGGEST THAT AMOUNTS WILL
BE FAIRLY LIGHT AND COVERAGE MIGHT BE SPOTTY. MCDONNAL
.LONG TERM...THE UPPER SHORTWAVE THAT MOVES INTO WESTERN WASHINGTON
SUNDAY NIGHT WILL MAINTAIN A CHANCE OF SHOWERS MONDAY AND MONDAY
NIGHT...BUT AGAIN AMOUNTS LOOK LIGHT AND COVERAGE SHOULD BE SPOTTY.
DRY NORTHERLY FLOW WILL TAKE OVER AGAIN TUESDAY AHEAD OF A STRONG
UPPER RIDGE OFFSHORE OUTSIDE OF 130W. THE UPPER RIDGE WILL MOVE
SLOWLY TOWARD THE REGION FOR ANOTHER DRY DAY WEDNESDAY. IT WILL
WEAKEN AS IT MOVES INLAND THURSDAY...AND A WEAK SYSTEM MOVING OVER
THE NORTH SIDE OF THE RIDGE COULD BRING SOME PRECIPITATION TO
WESTERN WASHINGTON. THE MODELS ALL AGREE ON THIS GENERAL SCENARIO.
MCDONNAL
&&
.HYDROLOGY...FLOODING IS UNLIKELY FOR THE NEXT 7 DAYS.
&&
.AVIATION...A SURFACE AND UPPER LEVEL LOW IS DROPPING SOUTHWARD
ALONG THE WASHINGTON COAST EARLY THIS MORNING. THE LOW WILL DROPS
SOUTH THROUGH THE COASTAL WATERS OF OREGON TODAY. THE AIR MASS IS
MOIST AND STABLE ACROSS WESTERN WASHINGTON. NORTHEASTERLY FLOW OVER
THE FAR NORTHERN PORTIONS OF THE INTERIOR ARE GIVING VFR CONDITIONS
THERE. ELSEWHERE...RAIN AND LOW LEVEL CONVERGENCE IS GIVING MVFR
CEILINGS AND LOCAL IFR CONDITIONS. CONDITIONS WILL GRADUALLY IMPROVE
FROM THE NORTH THIS MORNING AND WILL BE VFR ACROSS THE AREA BY ABOUT
20Z. ALBRECHT
KSEA...EXPECT 4-6SM RABR BKN015-025 OVC035 THROUGH ABOUT 18Z.
CONDITIONS WILL IMPROVE TO P6SM SCT025 BKN050 BY ABOUT 22Z. E WIND
5-7 KT EARLY THIS MORNING WILL BECOME N 7-10 KT AROUND 15Z AND N
12G20KT BY 21Z. ALBRECHT
&&
.MARINE...A BROAD AND DIFFUSE LOW OVER THE WASHINGTON COASTAL WATERS
WILL DROP SOUTH THROUGH THE OREGON COASTAL WATERS TODAY. N TO NE
WINDS 15-25 KT WILL DEVELOP OVER ALL OF THE WATERS THROUGH THIS
AFTERNOON AS THE LOW DEPARTS AND A 1030-1035 MB HIGH DEVELOPS OVER
BRITISH COLUMBIA. PORTIONS OF THE STRAIT OF JUAN DE FUCA...THE
COASTAL WATERS ADJACENT TO THE STRAIT...AND THE NORTHERN INLAND
WATERS MAY SEE LOCAL 30 KT WINDS BY TONIGHT AND EARLY SATURDAY
MORNING. THE ONLY ZONE NOT IN A SMALL CRAFT ADVISORY THROUGH TODAY
WILL BE THE NEAR COASTAL WATERS FROM POINT GRENVILLE TO CAPE
SHOALWATER OUT TO 10 NM...WHERE CONVERGENT NORTH AND NORTHEAST WINDS
IN THAT AREA WILL KNOCK WIND SPEEDS BACK TODAY. A SMALL CRAFT
ADVISORY WILL LIKELY BE NEEDED FOR THAT ZONE TONIGHT.
WINDS WILL DIMINISH AND BECOME LIGHT ON SUN AS A RIDGE OF HIGH PRES
MOVES SE ACROSS THE WATERS. ANOTHER ROUND OF STRONG NE WINDS ARE
POSSIBLE LATER MON INTO TUE AS A 1040 MB HIGH BUILDS OVER BRITISH
COLUMBIA...THEN MOVES BY THE AREA TO THE NE. HOWEVER FORECAST MODELS
ARE TRENDING WEAKER WITH THE OUTFLOW FOR LATER MON INTO TUE. ALBRECHT
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY ALL WATERS EXCEPT FOR THE COASTAL WATERS
FROM POINT GRENVILLE TO CAPE SHOALWATER OUT TO 10 NM.
&&
$$
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